Effects of drug-induced changes in resting blood pressure on classically conditioned heart rate and blood pressure in restrained rats.

Subsequent to receiving aversive classical conditioning, which led to a decelerative heart rate (HR) conditioned response (CR) and a pressor-depressor blood pressure (BP) CR, three separate groups of restrained rats received intravenous infusion of sodium nitroprusside (40 micrograms/mg/min) to lower baseline BP, phenylephrine (17 micrograms/mg/min) to raise baseline BP, or an equivalent volume of saline. Conditioning test trials during infusion revealed that hypotension produced by sodium nitroprusside eliminated the HR CR and transformed the BP CR into a pressor-only reaction. Hypertension produced by phenylephrine facilitated the HR CR and changed the BP CR to a pressor-only response on selected trials in which baseline BP increases and baseline HR decreases were within restricted limits. Following drug withdrawal, the HR CRs of both drug groups and the BP CR of the phenylephrine group were attenuated. The unconditioned responses to the shock unconditioned stimulus under phenylephrine were exaggerated and consisted of tachycardias and depressor BP changes, whereas under sodium nitroprusside reduced tachycardias and depressor activity occurred. The results suggested that the loss of the vagally mediated HR CR under sodium nitroprusside was due to baroreceptor-controlled inhibition of vagal discharge and that the enhancement of the HR CR under phenylephrine was due to baroreceptor-influenced facilitation of vagal discharge.

[1]  S. Chien,et al.  Baroreflex control of heart rate in humans during nitroprusside-induced hypotension. , 1982, The American journal of physiology.

[2]  S. Chien,et al.  Resetting of Baroreflex Sensitivity after Induced Hypotension , 1982, Anesthesiology.

[3]  Thomas L. Smith,et al.  TECHNIQUES FOR TWENTY-FOUR HOUR HEMODYNAMIC MONITORING IN UNANESTHETIZED RATS , 1982 .

[4]  P. Schmid,et al.  Pressor response to vasopressin and impaired baroreflex function in DOC-salt hypertension. , 1982, The American journal of physiology.

[5]  D. Hatton,et al.  Autonomic control of heart rate and blood pressure in spontaneously hypertensive rats during aversive classical conditioning. , 1981, Journal of comparative and physiological psychology.

[6]  J. R. Mcneill,et al.  Pressor Responsiveness and Cardiovascular Reflex Activity in Spontaneously Hypertensive and Normotensive Rats During Vasopressin Infusion , 1981, Journal of cardiovascular pharmacology.

[7]  A. Atkinson,et al.  The pharmacological basis of therapeutics. 6th ed: By Alfred Goodman Gilman, Louis S. Goodman, and Alfred Gilman. 1843 pp., $45.00. Macmillan Publishing Co., Inc., New York, New York, 1980 , 1981 .

[8]  E. Bush,et al.  Influence of dietary sodium on renin angiotensin system involvement in sodium nitroprusside hypotension in conscious rats. , 1981, The Journal of pharmacology and experimental therapeutics.

[9]  K. M. Spyer,et al.  Neural organisation and control of the baroreceptor reflex. , 1981, Reviews of physiology, biochemistry and pharmacology.

[10]  J. Iriuchijima,et al.  Transposition response, a cardiovascular response to change of habitat in the rat. , 1980, The Japanese journal of physiology.

[11]  R. Vollmer,et al.  Role of the renin-angiotensin system in the blood pressure rebound to sodium nitroprusside in the conscious rat. , 1979, European journal of pharmacology.

[12]  R. Fitzgerald,et al.  Classically conditioned heart rate and blood pressure in rats based on either electric shock or ammonia fumes reinforcement , 1978, Physiology & Behavior.

[13]  J D Michenfelder,et al.  Sodium Nitroprusside: Pharmacology, Toxicology and Therapeutics , 1976, Anesthesiology.

[14]  G. Martin,et al.  Influence of vagal activity on classically conditioned heart rate in rats. , 1973, Journal of comparative and physiological psychology.

[15]  P. Wright,et al.  Species distribution of sympathetic cholinergic vasodilator nerves in skeletal muscle. , 1970, Acta physiologica Scandinavica.

[16]  N. Schneiderman,et al.  Vagal compensatory adjustment: relationship to heart rate classical conditioning in rabbits. , 1969, Journal of comparative and physiological psychology.

[17]  G. Mancia,et al.  Cardiovascular changes during naturally elicited fighting behavior in the cat. , 1969, The American journal of physiology.

[18]  G. Sutherland,et al.  The Circulatory Effects of Intravenous Phentolamine in Man , 1965, Circulation.